Polyphenol compounds are a class of organic compounds characterized by the presence of multiple phenol structural units. Thousands of naturally occurring polyphenol compounds are known, and the broad class of polyphenol compounds can be broken down into subgroups, such as flavonoids, which contain a 15 carbon atom scaffold comprising two aromatic rings linked by a three carbon bridge. The sub-class flavonoids can be broken down further to include compounds such as procyanidins, which are oligomeric compounds formed primarily from catechin and epicatechin molecules. One important class of non-flavonoid polyphenols are phenolic acids such as gallic acid, a precursor of hydrolysable tannins, such as ellagitannins.
Natural sources of polyphenols include common foodstuffs such as tea, coffee, cocoa, red wine, beer, cider, fruits, vegetables and nuts (Journal of Agricultural and Food Chemistry, 2010, 58: 4959-69). Other sources of polyphenols include plants that are generally not regarded as foodstuffs, but may be used as traditional herbal medicines, such as flowering plants of the Epilobium genus, commonly known as willowherb.
The endothelium is a single layer of cells lining every blood vessel. Maintaining healthy endothelial function is critical for overall health and wellbeing. Endothelial dysfunction is a common characteristic of altered cardiovascular function leading to coronary heart disease, and more generally atherothrombotic diseases including stroke and peripheral vascular disease. All risk factors for cardiovascular disease—raised LDL cholesterol, diabetes, smoking, high blood pressure (hypertension), increasing age and lack of exercise—have been linked to endothelial dysfunction. Endothelial dysfunction is widely recognised as a precursor to atherosclerotic lesion formation. Common characteristics of endothelial dysfunction include: increased inflammation; reductions in the healthy anti-thrombotic functions of the endothelium; increased synthesis of mediators that stimulate remodelling and vascular stiffness; and increased vasoconstriction with reduced vasodilatation.
Endothelial dysfunction is not only associated with the underlying mechanisms leading to cardiovascular disease, but also as a risk factor for cardiovascular events, including myocardial infarction. The severity of endothelial dysfunction is closely associated with increased risk of mortality in patients with chronic heart failure. Although statins and angiotensin-converting enzyme inhibitors cause modest improvements in endothelial function, there are currently no pharmaceutical medications that specifically treat endothelial dysfunction.
Nitric oxide (NO) plays a crucial role in normal endothelial function, including maintaining vascular homeostasis, modulation of vasodilator tone, regulation of local cell growth, and protection of the vessel from injurious consequences of platelets and cells circulating in blood. NO is continuously synthesized in endothelial cells by the enzyme nitric oxide synthase (eNOS). However, in patients with endothelial dysfunction, NO production can be impaired and endothelial dysfunction is often observed experimentally and clinically as reduced NO-dependent vasodilatation.
eNOS synthesizes nitric oxide using the amino acid L-arginine in the presence of the co-factor tetrahydrobiopterin (BH4). Recent approaches to the treatment of endothelial dysfunction have used both BH4 and L-arginine supplements in an attempt to boost production of NO. However, both of these approaches have drawbacks and lack reproducibility. In particular, BH4 readily oxidises to an inactive form, making it difficult to calculate how much of a given dose of BH4 is actually bioavailable to a patient in need thereof (Antioxidants and Redox Signaling, 2014, 20: 3040-77). The importance of BH4 has been further documented by overexpression of eNOS in mouse models, in which it was found that the resultant BH4—eNOS imbalance led to augmented formation of atherosclerotic lesions (Journal of Clinical Investigation, 2002, 110: 331-40). Moreover, the use of L-arginine supplements has been linked to higher post-infarction mortality, likely as a consequence of endothelial BH4 deficiency (Journal of the American Medical Association, 2006, 295: 58-64).
A further characteristic of endothelial dysfunction is increased synthesis of the vasoconstrictor peptide endothelin-1. Antagonists of endothelin-1 cause vasodilation and improve endothelium-dependent vasodilator responses in older people (Clinical Science, 2011, 120: 485-9), and in patients with atherosclerosis (Circulation, 2010, 122: 958-66).
Research on reversing endothelial dysfunction has identified the transcription factor Kruppel-like factor 2 (KLF2) as a key regulator of healthy endothelium, which affords protection from atherosclerosis. It has been proposed that agents that increase KLF2 in the endothelium could be used to treat endothelial dysfunction (Cardiovascular Pathology, 2013; 22:9-15). Some procyanidins are known to increase KLF2 transiently for a few hours (Journal of Agricultural & Food Chemistry, 2010; 58:4008-4013). Identification of agents that could sustain this induction would have greater therapeutic utility in restoring or maintaining endothelial function.
The effects of dietary polyphenols on vascular function have been investigated for more than 50 years. Hawthorn berry extract has been used for centuries as a treatment for cardiovascular disease including chronic heart failure (Journal of Clinical Pharmacology, 2002, 42: 605-12). The beneficial effects on cardiac function have been attributed to the high content of flavanols, principally procyanidins. High flavanol cocoa drinks and high flavanol dark chocolate have been found to improve endothelial function in patients with chronic heart failure, coronary artery disease, and diabetes (European Heart Journal, 2012, 33: 2172-80; Journal of the American College of Cardiology, 2008, 51: 2141-9; Journal of the American College of Cardiology, 2010, 56: 218-24). Grape seed extract, which is also mainly composed of procyanidins, also lowers blood pressure (Metabolism Clinical and Experimental, 2009, 58: 1743-6) and improves vascular function (Journal of Biomedicine and Biotechnology, 2004, 5: 272-8). The improvement in cardiovascular function with products containing high amounts of procyanidins is consistent with studies on isolated vessels showing that purified procyanidins cause endothelium-dependent vasodilatation via NO release (U.S. Pat. No. 6,706,756 B1), and inhibit the synthesis of endothelin-1 (Journal of Agricultural and Food Chemistry, 2010, 58: 4008-13).
The anti-atherosclerotic actions of pomegranate juice (Punica Granatum) have been reported (U.S. Pat. No. 8,221,806 B2). Pomegranate juice and pomegranate fruit extract promote endothelium-dependent vasodilatation of isolated vessels (Nitric Oxide, 2007, 17: 50-4). The components responsible for these effects have not been described.
Previous human volunteer and patient studies specifically focusing on dietary polyphenols and their impact on endothelial dysfunction have been poorly executed. Studies that have claimed to investigate such compounds and their effects on cardiovascular health have used complex, poorly defined mixtures of compounds, such that it was impossible to attribute any overall health benefit to any one particular component. Moreover, many studies have only measured indirect effects, such as blood pressure, rather than looking at nitric oxide production or endothelin-1 synthesis. For example, Basu et al. investigated the effect on cardiovascular health of berries (Nutrition Reviews 2010, 68: 168-177), while Asgary et al. investigated the effects of pomegranate juice on blood pressure (ARYA Atherosclerosis, 2013, 9: 326-31). However, both berries and pomegranate juice contain a wide variety of compounds, including not only polyphenol compounds such as proanthocyanidins or ellagitannins but also other substances known to have health benefits such as vitamins, minerals and fibre. Thus, it is impossible to draw any clear conclusions from these studies regarding the effects of dietary polyphenols on nitric oxide production and endothelial dysfunction.
There is a need in the art for new treatments for endothelial dysfunction. In particular, it would be advantageous to provide new treatments for endothelial dysfunction comprising an optimised mixture of purified polyphenol compounds, since it is anticipated that the side-effect profile from such compositions would be favourable. Compounds that improve endothelial function are also expected to be useful ergogenic aids. Thus, the provision of new ergogenic compositions is a further aim of the present invention.